Force Newton?

[jajrussel]

I was recently reading the definition of the metric unit of force. I have read it before, but this time made the mistake of thinking about it, and realized I don't remember how it was determined.

[J.C.MacSwell]

It is the force required to accelerate 1 Kg by a metre per second, every second.

[Bignose]

And you can always remember that by F = ma. Newtons on left side... the kg m per s per s on the right hand side.

[studiot]

One thing to be careful of is the way the metric system handles the relationship between mass and force.

 

There are two units called the kilogramme.

 

Kilogramme of mass

 

Kilogramme of Force - this is not used much and not part of Systeme Internationale (SI).

 

Remembering that weight is a force and using the previous two posts we have

 

1 kilogramme (mass) weighs 1 x 10 = 10 Newtons

 

ie the force of gravity on 1 kg is 10N.

 

10 is a good enough factor for most things but use 9.81 if you prefer.

 

This is a reversal of the situation with imperial units where pounds usually refers to pounds force or pounds weight, not pounds mass.

Pounds, mass gives a force in poundals.

Edited January 29, 2017 by studiot

[jajrussel]

It is the force required to accelerate 1 Kg by a metre per second, every second.

☺ How? How did they apply the force? How did they move the one kilogram? They used one unit of force called a Newton, to move one kilogram of mass, one meter, within a one second time frame. How?

 

If I push or pull it I have to deal with friction. I could tie a scale to it and pick it up, but that seems wrong because the scale might tell me it weighs one kilogram, and I can assume I used one Newton of force to pick it up. I can measure off a meter, then try to take exactly one second to move it that far. Way to many assumptions. If the definition is true the only thing I can be sure of is that I used at least one Newton of force, so long as it weighs one kilogram, and I moved it one meter in one second.

 

What experiment was done that defined a Newton?

[Bender]

☺ How? How did they apply the force? How did they move the one kilogram? They used one unit of force called a Newton, to move one kilogram of mass, one meter, within a one second time frame. How?

 

If I push or pull it I have to deal with friction. I could tie a scale to it and pick it up, but that seems wrong because the scale might tell me it weighs one kilogram, and I can assume I used one Newton of force to pick it up. I can measure off a meter, then try to take exactly one second to move it that far. Way to many assumptions. If the definition is true the only thing I can be sure of is that I used at least one Newton of force, so long as it weighs one kilogram, and I moved it one meter in one second.

 

What experiment was done that defined a Newton?

There was no experiment done. It was defined by the formula stated above F=ma. Since kg, s and m are defined, that defines the Newton.

 

Now if you are asking about how to calibrate a force sensor, that depends on the required accuracy. The most convenient is with gravity and a well known weight.

[jajrussel]

There was no experiment done. It was defined by the formula stated above F=ma. Since kg, s and m are defined, that defines the Newton.

 

Now if you are asking about how to calibrate a force sensor, that depends on the required accuracy. The most convenient is with gravity and a well known weight.

Thanks, this would explain why I don't remember anything but the definition. Seems odd.

 

The formula seems to suggest that there should be an energy equivalent. When I start searching am I going to find one, or am I wrong in assuming an association between acceleration and c squared?

[Bender]

I know of no such association.

[Mordred]

Thanks, this would explain why I don't remember anything but the definition. Seems odd.

 

The formula seems to suggest that there should be an energy equivalent. When I start searching am I going to find one, or am I wrong in assuming an association between acceleration and c squared?

Joule

[swansont]

Way to many assumptions.

I thought you'd met physics before. Frictionless surfaces and all that.

[jajrussel]

I thought you'd met physics before. Frictionless surfaces and all that.

Okay, too many assumptions.

 

I'm sorry its the way my mind works. I see c squared, and think velocity change.

Edited January 30, 2017 by jajrussel

[Bender]

c squared is a constant.

[jajrussel]

c squared is a constant.

Dawning? E=mc^2 is not a kinetic equation?/has a different purpose?

 

A universe without time or distance?

 

A singularity?

 

Remove my imagination, then = At rest.

Edited January 31, 2017 by jajrussel

[Bender]

Dawning? E=mc^2 is not a kinetic equation?/has a different purpose?

It denotes the equivalence between mass and energy, which are fundamentally the same thing.

 

If you want to include kinetic energy, you have to use

[math]E=\gamma m c^2[/math]

where [math]\gamma[/math] is the Lorenz factor. and m the "rest mass". But it is only worth the trouble at relativistic speeds. At lower speeds and in absence of nuclear reactions, you can safely ignore [math]E=m c^2[/math].

 

I don't know what your other questions are about.

Edited January 31, 2017 by Bender

[jajrussel]

One thing to be careful of is the way the metric system handles the relationship between mass and force.

 

There are two units called the kilogramme.

 

Kilogramme of mass

 

Kilogramme of Force - this is not used much and not part of Systeme Internationale (SI).

 

Remembering that weight is a force and using the previous two posts we have

 

1 kilogramme (mass) weighs 1 x 10 = 10 Newtons

 

ie the force of gravity on 1 kg is 10N.

 

10 is a good enough factor for most things but use 9.81 if you prefer.

 

This is a reversal of the situation with imperial units where pounds usually refers to pounds force or pounds weight, not pounds mass.

Pounds, mass gives a force in poundals.

I am curious. If I push on a wall and the wall does not change direction/accelerate/move. By definition have I done anything other than push on a wall? Have I used force? Done work?

 

It seems to me that I remember reading that if I didn't actually accomplish anything then it couldn't be said that I had done anything. Now, thinking about this one kilogram of mass just sitting on the ground. It is not just sitting on the ground. It is adding to the planets mass.

 

This causes me to think that when I pushed on the wall I likely did something even if it wasn't readily apparent.

 

Note, I am trying too get comfortable with the metric system, but it hurts my head when I try to imagine dividing something up in to a hundred pieces. I see the pie in my head then say okay, how exactly am I going to do this? Personally I think the meter is to big. If I remember correctly the speed of light in a vacuum rounds to 1E9 feet per second and this seems to me a little more accurate than 300 kilometers per second. Then inches would be 12E9. For clarity I mean 1 billion, and 12 billion. I clarify because I once owned a calculator that held a different view of what the E stood for. I am assuming that there actually is a good reason I should learn the metric system with its many weird sounding prefixes, but if I remember corectly it seems to me that Newton did all right with London inches.

[Bender]

I am curious. If I push on a wall and the wall does not change direction/accelerate/move. By definition have I done anything other than push on a wall? Have I used force? Done work?

 

It seems to me that I remember reading that if I didn't actually accomplish anything then it couldn't be said that I had done anything. Now, thinking about this one kilogram of mass just sitting on the ground. It is not just sitting on the ground. It is adding to the planets mass.

 

This causes me to think that when I pushed on the wall I likely did something even if it wasn't readily apparent.

If a force is exerted without movement, no work is done.

[math]W=d \cdot F[/math]

where d is the distance moved, so if it is zero, the work is zero. You have expended energy, because your muscles consume energy even if they do not move. Gravity on the other hand is conservative, which means that it expends no energy when no work is done.

 

The kg of mass doesn't need to sit on the ground to add mass to the planet, it also adds its mass to the planet when it is in the air.

 

 

Note, I am trying too get comfortable with the metric system, but it hurts my head when I try to imagine dividing something up in to a hundred pieces. I see the pie in my head then say okay, how exactly am I going to do this? Personally I think the meter is to big. If I remember correctly the speed of light in a vacuum rounds to 1E9 feet per second and this seems to me a little more accurate than 300 kilometers per second. Then inches would be 12E9. For clarity I mean 1 billion, and 12 billion. I clarify because I once owned a calculator that held a different view of what the E stood for. I am assuming that there actually is a good reason I should learn the metric system with its many weird sounding prefixes, but if I remember corectly it seems to me that Newton did all right with London inches.

The only advantage the imperial system has over the metric system is that you are used to it. Calculating in 10's is much easier, the different units in the metric system are more consistently matched with each other, so you need less conversion factors, there are no multiple definitions of the same unit, the definitions of the imperial system is now even based on the metric system.

 

Also, the speed of light is 983 571 056 feet per second, so 1 billion ft/s is actually less accurate than 300 km/s.

Edited January 31, 2017 by Bender

[studiot]

 

 

The only advantage the imperial system has over the metric system is that you are used to it. Calculating in 10's is much easier,

 

When it comes to pints I find imperial measure far superior.

 

 

 

[Bender]

So you are a light drinker preferring a pint over a liter?

[imatfaal]

If a force is exerted without movement, no work is done.

[math]W=d \cdot F[/math]

where d is the distance moved, so if it is zero, the work is zero. You have expended energy, because your muscles consume energy even if they do not move. Gravity on the other hand is conservative, which means that it expends no energy when no work is done.

 

The kg of mass doesn't need to sit on the ground to add mass to the planet, it also adds its mass to the planet when it is in the air.

 

 

The only advantage the imperial system has over the metric system is that you are used to it. Calculating in 10's is much easier, the different units in the metric system are more consistently matched with each other, so you need less conversion factors, there are no multiple definitions of the same unit, the definitions of the imperial system is now even based on the metric system.

 

Also, the speed of light is 983 571 056 feet per second, so 1 billion ft/s is actually less accurate than 300 km/s.

 

Hmm

Speed of light 9.836e8 feet per second - 1e9 feet per second is a roughly 2 in a hundred error

Speed of light 2.998e8 m/s - 300km/s is a 3 orders of magnitude error! Typos aside 300,000 km/s is roughly 2 in 3000 error - so much more accurate